Most inherited cases of breast cancer have been associated with two genes: BRCA1, which stands for BReast CAncer gene one, and BRCA2, or BReast CAncer gene two. Women with an abnormal BRCA1 or BRCA2 gene have up to an 85% risk of developing breast cancer by age 70. Abnormal BRCA1 and BRCA2 genes are found in 5% to 10% of all breast cancer cases in the United States.

A study found that women with an abnormal BRCA1 gene had a worse prognosis than women with an abnormal BRCA2 gene 5 years after diagnosis. Women with an abnormal BRCA2 gene had a prognosis that was basically the same as women with no abnormal breast cancer genes 5 years after diagnosis. Five years after diagnosis:

73% of women with an abnormal BRCA1 gene were alive

96% of women with an abnormal BRCA2 gene were alive

92% of women with no abnormal breast cancer genes were alive

The researchers suggest that this difference in prognosis should be considered when deciding on treatment for women with an abnormal BRCA1 gene.

Another study found that women with an abnormal BRCA1 or BRCA2 gene have the same prognosis as women who don't have abnormal breast cancer genes 10 years after diagnosis (5 more years after diagnosis than the study reviewed here). There are several possible reasons why these two studies seem to have different results:

It might be that women with an abnormal BRCA1 gene have a worse prognosis in the first 5 years after diagnosis, but do better in the next 5 years so their overall prognosis at 10 years is the same as women with an abnormal BRCA2 gene or no abnormal genes.

The study reviewed here is small. There were only 89 women with an abnormal BRCA1 gene and only 35 women with an abnormal BRCA2 gene. The results of this study may have been different if more women with abnormal breast cancer genes were followed.

There may have been other differences between the women that influenced the results.

If you have an abnormal BRCA1 or BRCA2 gene, your risk of developing breast cancer is higher than the average woman's. You can't change your genetics. But you can make sure that if breast cancer develops it is diagnosed as early as possible. You and your doctor should develop a special screening plan that includes more frequent screenings starting at an early age, and possibly MRI scans or other screening techniques. Abnormal breast cancer genes also increase the risk of ovarian cancer, so it's important to discuss this with your doctor, too. To learn more, visit the Breastcancer.org Breast Cancer Risk Factors: Genetics page.